This project proposes a set of lab and field experiments to further the fundamental understanding of[unreadable] biogeochemical processes governing the behavior and transport of inorganic and organic Arsenic (As)[unreadable] species as well as contribute to the design and management of remediation activities of sites contaminated[unreadable] with As. We have chosen the Vineland Chemical site in southern New Jersey as our primary field site[unreadable] because it offers a number of research opportunities. One primary focus will be on experiments that could[unreadable] help optimize pump and treat operations. These studies would include plume capture efficiency assessments[unreadable] through measurements of tracers of groundwater flow velocities and directions. They would also involve[unreadable] laboratory and field experiments to investigate whether manipulations of aquifer chemistry could enhance[unreadable] remediation of groundwater As, primarily through accelerating As mobilization from aquifer solids, thereby[unreadable] enabling pump and treat operations to decrease subsurface As inventories more rapidly. We will also[unreadable] collaborate with Project 7 on investigating the feasibility of using permeable reactive barriers of zero valent[unreadable] iron as an additional remediation strategy to the current pump and treat system.[unreadable] Other field experiments will investigate fundamental transport and fate issues of As in two offsite areas[unreadable] highly contaminated with As, specifically the Blackwater Branch and Union Lake. We will further investigate[unreadable] As cycling in bottom sediments of both the stream (which runs adjacent to the Superfund site) and of Union[unreadable] Lake. Our prior work has shown that the sediments of these two surface water bodies have dramatically[unreadable] different As chemistries, with fine-grained sediments of the stream having As controlled largely by sulfur[unreadable] chemistry while As in the lake sediments appears to be primarily controlled by iron chemistry. Additional[unreadable] sediment-porewater research will be done in the Blackwater Branch to investigate whether As behavior[unreadable] changes as a function of streamflow/groundwater discharge rates and to investigate As porewater-sediment[unreadable] interactions in sandy sediments which represent >80% of the stream bottom. The role of storm events in[unreadable] transporting As in the Blackwater Branch will also be investigated. Finally, research in Union Lake will[unreadable] investigate the magnitude of As release from sediments during episodes of anoxia in bottom waters.